Underreamer



Sept. 20, 1932.

F. s. BUNKER 1,878,260

UNDERREAMER Filed Feb. A12, 1929A 2 Sheets-Sheet 1 F. S. BUNKER sept. z, 1932.

UNDERREAMER Filed Feb. l2. 1929 2 Sheets-Sheet 2 'Patented Sept. 20, Y l

The presentv vinvention 'f concerned generf ally With `expansive `drills or rearners vfor use iiivvell drilling operatiomand relates particuf larly tounder reainers for enltijgiiigV avvell V5 bore below the casing, and'for use'ln` comble; L

lo tvveen the cutters; and acting asf a wedge t expand the cuttersvvhen-they moveupvvardly` vvith'relation to theinternaleore. This Char#` acterist-ic otinventioii mayV 4be applicable to manydift'erent -formsiof expansible reamers-Qr ,Y

nnderreamer's, and consequentlyl do lnot Wish to be understoodas :limiting the inventionto the particular f form. .of underreamer which apparatus, No. I1,678,073 issuednluly'24,;1928; and therefore I shall explain theinvention reterencextothecentralmandrelor core; and

the tool beingfso shaped that.by:.vvedgfing` i f e i lnthe dravvingafthe reamer generally indi- 80 A t catedat'lO;isshownattachedfto theipilot drilll Asi applied to that. `particulartype of eX- pansi'vetool7 mv .invention involves not only they aremovedfupvvardly.; 1 n

action, .j the t cutters "move: loutwardly relatively longitudinalfmovfement and Wedge `35` action between the cuttersland--core`,`foreiny paladini@ the former, lbut also longitudinalV portionorcorerforthepurposeof takingup 'Y anvlo'osenes's' orlr'vvear fand thus keepingthe cutter" ti ghtly hield fat all: times.A Preferably` the adiustment (if-: the vcore; is i automatic and 'biv.' -springactnation i *y L j ?TheEabovelcharacteristics of ,the invention i panying dravvingsinvvhich.: t

` ,59 EigLisa;centralflongitudinal ont?ron; CALIFonnIA.

mamma by ade` Y justable movable internalfcoretor mandrel# l portion -acting' as aninternal abutment be- Y itself very t*readilyftoexpansive reamers' of the type shownin the Phipps patent on vv'ell as applied to that type'ofytool. Ezpandingi reamers ofthattype involvefa central; man. drel ori abutment icore between 1 the eutteris, 'f 'the cutters .being movable zverticallyil with Application filed'Februar"yfrz,1929.1y serial Nb. 3s9,z a5,

1 an underreamer inaocordancevviththepresy f l entjnven'tiomthe;cutterbei'ngshowningcongg tralctedlposition, yand a drillbeingattachedl i tothefreamem"jf-i'.gf ggf t, 1i Fig. 2 isa-view simlarto Fig. 1- but show-y 55 :ingthefcutters inv expanded position gr, i Figg 3l is La cross section on lnesj-fof 23am Y' l i e '-Fig. ,55 is;` a vieW generallygsimilarto lFig-J Q'jb'ut[showinga. variational yiormgotoutter i actuatingmeans; v Although inthe present 'embodiment ofthe j tudnally'l relatively/5to the bodvand cutter.

v, expanding -vvedgegfit Will beY apparentthat'f f this may not necessarily be `*the case insofar i Sas therelativemovementsofthe WedgeV and'ro j Y .'c'utteris concerned, forthej expanding-action "V of the cutter is'dependent'uponrelative move-i A l.ment between thecutter and. Wedgeeore and' n otgbetvveen'the Vcore .and body*V Therefore5 inf-its broader aspects',r theiinvention relates V75l i toft'ools'- ioi vthis{character-VWhereinrthe-Edelscribed@relative movements between the .cut-j Y, e f yterstakes place, irrespective off the relative bit '1 1,j thefbitpin 11a being threaded into the]v plower reduced portion 12a/ofthe reamerbar: Y rel 12'.V A mandrel 13 'extendscentrally with-f in 'thegbodm theenlarged :head-13a; ot the 853 mandrelbe`3 i`11, fthreadedatil'intothe uper Y 1 fend "offthebodv, the mandrel 'in turn bein-g f Vjoined to the drillpipe' Collar'l;4 The reduced portions-13b,v13c "13Z,.of the'man'dreldepend" Y v: Y'Withinithebodvrorntheheadiportion 13215,: 99 `l"` the-lower-endtbfetheimandrel beingspacedat `16a suitable! distance fromthe bitipin 11a; A'uidjpassage 17, communicatingvvith the v Y drill'jpipe -interior',` extendscontinuously i. .f .fthroughthe :mandrel-t0'onengintospace 16519? l.

and a`. conm'arativelvl smaller passagelexf tendsvvithin hthedrill and servesfto discharge fluid from'space 16 throughthebit, i Y' f CutterslotsQO, vthree being-shown, @are `formed longitudinallyin the `barrel,V ,thejslots 19@ 1 invention the body ofthe weiterem-Wely165: stationary,;an`d thecutters are movable longi'! Y io around the sides of the cutter.

being arranged symmetrically about the mandrel. The slots carry the radially and longitudinally movable cutters 2l, the increased length of the slots being that necessary. to permit the desired longitudinal movement of the cutter. 1t will be noted that the sides of the cutters bear flatly at 22 against the sides of the slots, this being desired in order to provide maximum lateral backing. for the cutter within the body and to preventftheentrance of well liquid to the interior of 'the reamer The cutters are here shown in the form of vblade cutters having vertical cutting edges 24, and recesses on their faces at 23, but it will be understood that the cutters may be made in any form desired. The cutters have thev inner inclined wedge faces 26 and are adapted to provide the longitudinally extending flanges-21o adapted tobear against the inclined portion 27 of the inner body wall when the cutters are in the positions indicated at Fig. 2. The iianged portions obviously limit the outward movement of the cutters and prevent their removal u: outward through the slot. n y* The cutters are caused to move radially out-v ward to expanded position by virtue of their upward movement relative to the downwardly'tapered mandrel element orrwedge core 30, the latter being slidably mounted on the man drel and adapted to bear against the inner wedge faces 26 of the cutters at all times. Spring 31 is interposed between the .wedge core and the mandrel shoulder 32 and serves to urge the core into engagement with the cutters at all positions thereof. .Thus the core may be considered as being vertically and automatically adjustable to compensate for u by spring 3l', and since the inclined portion wear of the engaging wedge surfaces, and to assure proper expansion of the cutters even after the engaging surfaces have become severely worn. Itis desirable that thewedge faces of the core be shaped to enable the inner ends of the cutter to bear substantially flatly therea'gainst, and yet preclude the possibility of the core turning within the body vso VVas toi bring the wedge surfaces ofthe cutter and core out of register. -Acco-rdingly, I have formed rectangular slots in one, adapted vto take similarly sha-pedfprojections on the other, and although it is immaterial upon which the proj ections-and grooves areformed, l have, in thepresent instance, provided grooves 38 in the cutter to take' projections 30a extending longitudinally on thecore.' in the drawings, one of the cutters has been omitted to illustrate the core projections more clearly. 1 W

lt will be noted that during themovement of the cutter `between the positions shown, no appreciable vertical movementof the core on the mandrel takes place. That this is actually the case will be apparent thatsubstantial upward movement o fthe'core is prevented 27 of the inner wall surface yand the engaging wedge faces of both the cutters and the core extending parallel in all positions of the cutters, it is evident that downward movement of the core cannot take place upon either upward or downward movement of the cutters. insofar as the wedge action between the cut-` ters and core is concerned, it will readily be seen that the mandrel serves mainly as a mounting and guide for the core. Preferably,

vthe mandrel takes substantially no stress impartedto the wedge coreby the cutters, and it may be desirable for the core to more or less loosely fit the mandrel in order that forces may be transmitted between cutters directly throughthe wedge without imposing strain on the mandrel.` Insofar as the expansion and contraction actions of the cutters is concerned, the mandrel part 1.30 might be eliminated, butit serves very readily as a guide for the wedgel, and alsoas av circula tion duct to carry the circulation fluid longitudinally through the tool. v

It may be stated that theangle of the wedge core 30 should be suicient to give the desired cutter eXpansion'upon upward move mentv ofithe cutter within reasonable limits, and that the wedge angle should be sufficiently. large that there is no markedY tendency of the cutters to move upwardly and wedge automatically by reason of their frictional engagement `with the well casing as the tool is lowered. The wedge angle may be varied, and can be` increased over vthat shown, to take care of any tendency of the cutters to wedge in the pipeor hole. It will be noted,`however, that since the wedge is pressed downward byspring 8l, the spring preferably being i strong, the wedgev first clamps .the cutter by wedging action between the wedge and body wall, this Lbeing' an effective deterrent in preventing the cutters fro-m moving up and wedging outwardly.

In order to prevent the entrance of well fluid 'to the tube through the upper portions of the slot when the cutters are in contracted positions, I have provided a protector sleeve 35, the lower edge of which rests flatly on the tops of the cutters. The upper and outer cylindrical surface 35a of the sleeve has a snug sliding fit within the upper cylindrical portion 27a of the body bore, the inclined surface 36aV of the sleeve being adapted to snugly fit the inclined bore wall 27 when the parts are in the position shown in Fig. 1. The sleeve is caused to seat firmly on the cutter by means of a relatively weak spring 38 seated in an annular recess 35?) within the sleeve and bearing upwardly against the mandrel head. Thus the protector sleeve follows the cutters through their vertical movement and prevents the entrance ofrfluid carrying abrasive particles that would cause -undue wear on the interior parts of the tool. This featureinvolving the use of the protector sleeve, howp ever, is not linvenitibn; but is included under the subjectmatterfofja eopending- `applicationfby' John-Grant onfprotected-reamer,

senno; 260,713, 2iilea-'lwan 1o .1928; 1

p inclined' -surface 2751 is cylindrically shaped and' provides a plunger chamber "tofcontain the plunger `40;` and fthepropeller 141; The.

prop'eller41- has aplungerftwith tliejcham-l .ber Wall 272) andV is adapted to slideglongitudinally along the? mandrel portion 13C and to engagev the] lower Vends of the cutter-fio move them upwardlywithin theslots-and v into Wedgingengagementwith the core. lIt p will be notedV Whenthef'cuttersfareT in eX# panded `position,` Y the propeller ei'ective'ly lprevents'the entrance 'ot large solid particles fromthe Wel-lfto the tool interior. Plung- 'fer 40is adapted to' slidealong fthe `tool `in-V terior.` Plunger 40 is adapted toslide along the lowermost portion-13d of themandrel, `v

theV plunger providedvvith suitable packing or rings-40a t0. prevent lthe escape,` around the plunger,` of actuating fluid, deli-vered to chamberrCthrough 1*;hemandrel.V

v Fluid passages 42 are-formed'in the I"body and'extend freni Aintermediatei, points'.iinrthe sidesv of theplunger chai'nber Walltojthe *36 vlower inclined.' "ends 20ml kof Vthe body slots,

the-j purpose of these passagesbeing todis'- charge a certainaniount of circulating- Huid into the Working 'region 'of cutters -dur-4 ing 'reamingfoperationsg Asfshovvn f in Fig. '2; passages LQ/.open intojthe plunger; chamber to be --iuncovered by. fthe plunger only Vvvhen the? lattery isf in its iupper `position i and the cutters` are, expanded;V The combined cross section 'area -ofthese passages-1s, as.

will "be seen, less than the area lofi'theinan drel bore-17.** f t .YIntheembadimeaeefmyfiiiveaaa hewn i inFigsgAl landr-'the plunger and cutter propeller'are actuatedlbvfluid pressure infchamber C; and'pin'this'vregardeit Willffbe noted. that Huid vpassa-gejlS in the drill jbit fis com# paratively! smaller` than fthe", frnandrel bore 171 The relative sizes "of thesepassagesV are j suchl thatfupon dischargeV .offiflfuid through upward and to'hold the cutters in expanded position; When Ythe plunger',` raises to un# cover 4the lluid `passages`42, eirculatingpuid is discharged belowl thelcuttersf but-.these 1 l passages are of suchsiaeasftofrestrict' lthe flow'V `from chamber fsulliciently j"tof retain suitable pressure o nrthe'z lower end :of the maintain p the fcutte'rs in expanded -pesition` Y During the loweringgofj "the Vtool assemblyg` through the casing (not-shownlthecutters fluid being pumped through the "mandrel to? readily Within thecasing.

Vaetuate1theplunger, .'Whenf'the-toolis loin-'3:V f5 i i 'ered to the Working region below the casing,4 ,Y

ho'vveverffthe @actuating lliuid is pumped through Lthef-mandrel tofexpandthe cutters, f o mentioned,'1l during 4oper ation the' circulating .fluid-Vis dischargedfat'the Working regions ofY thegcutters and thedrillbitthrough passages y 42falnd' 18, respectively. `llo remove thejftool j .5,V `;fluidthroughtheniandrelfisstopped andthe? from, the Well, pumping of the--fcirculating cutters permitted to lower to contractedlposi;l

V,tion either bvvi'rtue of theirovvn Weightrorj- 1J..v by'engagement',Withthe.lovver end of the".v `rcasing -'s`hoe,`,the upper corners of 'the-cutter .being rounded at 210.1toenable thenrtofv The forma of the`nvent'ion"shownin i with respect to Vthe cutteractuating :means More specically,-'inthis' embodiment', :the f foperation,of` thevtorol insofarasfactuatingthe-f v Y. cutters is `rconcerned,fis not' r` dependent upon-Y '90" fluid pressure-, and. althoughT-luidintre# duced to ithetool as vinthel previous: instance V5V is generallysimilarto'thepreviouslvde1 l scribed embodiment, Abut differs vsomewhat 8,5 f'

.andtheiiudrpressure;inlitsel'J inlay besuf- 'i Y i ficientzto'a'ctuate the'cutters, operationolftlie l '-'latteris assured should the fluid pressure-be no more* than that? inecessary lellect the 'desiredcireulationg- I11:Fig.`f5,the flower portion r12.03 the` 'i bodylzpreferably is elongated'somevvhatto n provide for vtaking the vspring46,`v the spring plungerf40' intheV previously described type 1 iee-v L sheulderf47vjandthe `propellerfplungerV 45;.' if' being dispensed with.' ormally-thekjcutters are "held ingtheir upperf'expanded.posil tion duetothe action olf-spring 46,5thespri`ng 1051 'providing an'upwardthrust onthe propeller l infadditiontojthe*luidlpressure.onfits lovver v into Y communication vv'ith theIV cylindrical s'rce-...j The'jv spring islet. such strength, *hows ,e f. ever, that its1upWard',thrustfis,Y in. itself, sufxl Vfi''ent""tei .hold fthjey'fcnaersexpanded, and.; y y Y thffrelh'futteis iarfirositionedregard? I less'oi'rthefluid pressure.y .lnthis'form5 pas-j J Vfsages 42- are covered byvrthepropeller when l. Hermes' fire'l consacre-ami; .are nought* Y Y A chamber C Whentheparts are inthe posi;v

tion" shown.` "As-.fin the "previous V-linstancegv'A passages 42 rservk-'i'vft'o directfluid'i discharged y into thechamberfromjthe -1nandrel against the cutters, ,and circulation A`tothe bity takes' placethrough..4 passage 18; @bviously "it is v'necessary lto :contract p the-cutters' .Whenfy the toolisfinserted fori lowering Within. the y"cas .f ing,` the cutters learingagainst. the casing through. i lZVhfe'nl 'ther tool passesV the.V lovverv end'olthe casinggthe'cuttersjeo course are L released toiiInOve toftheir: 'evpandedfposition arein the' contracted position ofLFiga 1,-l no" I The :formof tolfshown `i kie it may not be desiredto impart a strong positive thrust against the propeller to expand the cutters, but to cause their expansion at the working region by virtue of their engagement with a barrier or a shoulder formed in the well bore at the top of the underreamed portion. Under these conditions relative vertical movement of thel cutters is caused by their being retarded by the bore restriction or shoulder,-wliile the body of the tool and the wedge core moveV downward, the latter serving to expand the cutters. ln this case spring 46 would not serve to expand the cutters as in the previous case, but merely to support the propeller beneath'the cutters to prevent the entrance of well fiuid to chamber C. Also spring 3l would be tensioned so as not to cause the cutters to expand, `but onlyv to compensate for wear on the cutters as in the previous instance.

I claim: Y

l. An underreamer having a vertical tubular slotted body, a central mandrel extending vertically through the longitudinal bore of the body, a cutter movable radially and longitudinally in the body slot, a wedge core mounted on said mandrel and adapted lto yieldably engage the cutter, said core being substantially vertically stationary on the mandrel, and lmeans for'moving the cutter longitudinally against said core to cause the cutter to move radially in the slot.

2. An underreamer having a vertical tubular slotted body, a central mandrel extending if vertically through the longitudinal bore of the body, a cutter movable radially and longitudinally in the body slot, a vertically adjustable core. mounted on said mandrel `and adapted to engage the cutter, means on said core and cutter preventing their relative lateral movement, saidmeans embodying a projection on one adapted to extend within a recess in the other, and means for moving ,the cutter longitudinally against the core.

3. An underreamer having avertical tubular slotted body, a central mandrel extending verticallylthrough the longitudinal bore of the body, a cutter movable radially and longitudinally in the body slot,.said cutter having an inner inclined wedge face, a downwardly Y tapered wedge core slidably mounted on said mandrel and adapted to engage said wedge face of the cutter, yielding means urging said wedge coreY downwardly to engage the cutters, a propellerA on the mandrel below the' Vcore and adapted toengage the lower end of the cutter, and means for moving said propeller upward to bring said cutter into wedging engagement with thek core. I

4. An underreamer having avertical tubular slotted body, acentral tubular mandrel extending vertically through the 'longitudinal bore of the body, a cutter adapted to move radially and longitudinally in the body slot, a vertically adjustable wedge core mounted on the mandrel and adapted'to engage the cut-ter, said corey normally being substantially ,vertically vstationary on the mandrel,and means onmoving said cutter upwardly against the core by virtue of fluid pressure directed through the mandrel.

5. An ,underreamer having a vertical tubular slotted body, a central tubular .mandrel extending vertically through the longitudinal bore ofthe body, a cutter'adapted to move radially and longitudinally in the body slot, a vertically adjustable. wedgecore mounted on the mandrel'and'adapted to engage the cutter, said'core normally-being substantially vertically stationary on the mandrel, means preventing relative lateral movement between the coreand cutter, .and means for moving said cutter upwardly against the core by virtue of fluid pressure directed through the mandrel.

6i Inl an underreamena vertical tubular slotted body, a central tubular mandrel extending vertically through the longitudinal bore of the body and adapted to discharge fluid into the lower end thereof, a cutter adaptedV to' ino-ve radially and longitudinally in thebody slot, a vertically adjustable wedge core mounted on the mandrel and adapted to .engage the cutter, a tubular propeller slidably mountedl on the mandrel below said wedge` and adapted to engage the lower end 'ofy the cutter, a plunger slidably mounted on they inandrelbelow said propeller, and a fluid outlet in the mandrel below the-plunger, said plunger being adapted to loe-forced upwardly by fluid pressure andito` actuate said cutter through the propeller. v e

1 7. In an underreamer, a vertical tubular slotted body, .av central tubular mandrel extending vertically through the longitudinal bore of the body and adapted to discharge fluid into the lower end thereof, a cutter movable radially vand longitudinally in the body slot, al vertically adjustable wedge core mounted on the mandrel and adapted to engage thecutter, aplungerslidably mounted on themandrel below said core, a comparatively large lfluid outlet in the mandrel below the plunger, and a comparatively small fluid discharge opening through the barrel below said plunger, `the plunger being forced upwardly to actuate the cutter by fluid pressure developed byvirtue of the differential in size between said iluid outlet and the discharge opening. 8. In an underreamer, a vertical tubular slotted body, a central tubular mandrel extending vertically through the longitudinal bore of the body and adapted to discharge fluid into a plunger chamber in the lower end thereof, a cutter movableV radially and longitudinally in the body slot,ra vertically adjustabe wedge core mounted on the mandrel and adapted to engage the cutter, a vertically movable plunger on the mandrel below vthe i i 1,378,26()Y Y' i 'coreana insaiaehambea a liquideuuala Y the mandrel belovv'the plunger, said plunger being adapted to "be forcedupvvardlyby luid -pressure to"actuatef the cutter, and-a vfluid passage through the, body :Wall andadapted todircct fluid from said chamberto the Worl-` ,1

ingregion of the cutters, saidpassage being v1n communication fvvith thef--chamberjvvhe'n the plunger is in its upper position.A i9. Inan underreamer, the combinationv ofkv a vertical tubular slotted body, a tool'threader Y ed into the lowerend 'of said-body, a central tubular mandrel extendinglvertically through v the longitudinal bore of the bodyeandtermi-` nat-ing above 'the lowere'nd thereof, a plunger chamber inthe loWerportion of: the barrel and about the lower `end of" the mandrel, a

"cutter movable radially and longitudinally in the bodyslot,a Wedge core mounted 'on'ithe mandrel Vand l adapted to y-yield'aloly engage the cutter, a vertically: movable plungerv mounted on the-mandrelbelovv'said core andV Within said" chamber, 'a -comparatively'large ,i opening inthe mandrel or dischargingtluid l throughv the'inandrel into ksaid `chamber beloW the plunger, and a comparativelysmall 1 discharge openlngiin saidtool forconducting. fluid vromthe chamber, said plunger being actuated by luid'r-pressure Vdeveloped ,by vir@ tue of the diiferentialsin size betyveenfsaid;

openings. p

l0. In a reamer Y y Y a'longitudinally slotted tubularjbody, cutters movablefradially and longitudinallyfgin the body slots, VaV vertically adjustable Wedge core Within said'bodyand adapted tofengagethe Y Y cutters, `meant for :effecting relative longi-V tudinal movementbetween thecore andcuty ters toy cause theflatterl to move radiallyinthe slots,fand a vertically movable sleeve Within n thebarrel and resting atits lower gend on the upper ends of the'cutt'ers,-said sleeve being Y adaptedtoclose the. ,up-per vends of the'slotsf' Vwhen the cutters are in their lower positions. l,

11. An'underreamer havinga vertical .tubular slottedbody,a central mandrel extending vertically through the longitudinalzboreof Y the body, a Cutter movable radially and longi;

tudinally in the body slot, said cutter having i van inner inclined wedge face, a dovvnvvardlyi j Y tapered wedge corelslidably mounted on said 1 tf1-the har-aaa detained;

ter inone longitudinal direction causes transf? i versemovement ofthe cutter,'means1to lmove i `the'ftm'tter longitudinallyinsaidjldirection, f and meanstofmoveA th'evvedge in thefopposite i) longitudinaldirection, t Y Y ,n v y ,ffllgIn anunderreamenja body,ffa cutter movable longitudinallyl andvtransversely WitliV relationfto the }body, 'a longitudinally mo'vf.` ,y :able cutter spreading Wedge vin the body be-gVv 1 hind the cutter, the cutter l and Wedge being formedso that relative movement of the cut-4 .ter inonelongitudinal directionoauses transf l Y verse 'movement offtheutter,` fluid-pressure `actuated means to move the' t cutter longi tudinally inl said.V direction, 'andfspring means nal clirectionl'V y 'diagonal' cutter guide, a cutter movable along saidV guide, a longitudinally :movablel cutterv spreading'vvedge in th-ebody behind-the cuti i to move' the Wedge inftheoppositelongitudi- Y 1 14.-',In anlfunderreamer, afbody having aL i ter and havinga'v vvedgel facegsubstantially i larger endothe Wedge,andmeans togmove therein,- a' vertically 'Inova-ble" cutterspreading 16.2Inlan underreamer, a vertical body, a

cutter vmovable vertically and 'transversely i Y i Y therein, a. verticallyyielding cutter spreading` Wedge; in the body behind thefcutter parallel to the' -diagonal cutter guide,"me"ansv to. y move the cutter longitudinallyetoward lthe 1;. 9o Y the, Wedgellongitudinally inthe opposite'di-`` 4 r rection.` f 1 f y 1 .i

adapted tofcause outvvard'expan'sive move? ment ofthecutter when thejcutterisfmoved I up-Wardlya nd meansacting on the-cutter toi y *y In WitnessjthatI claim the foregoing I y Vhave hereunto subscribed-my name this'Q'day of February, 1929. 1

mandrel and adaptedto engage said vvedge fi I 4 lace of the cutter, yielding means urging said l Y -Wedge core downwardlytoengage the'cutQ M Y.

ters, means for movingsaid propeller upward Y y f .i to bring saidjcutterintofwedging'engagement withthe c'ore,sa id bodylfhaving` inclined cut- V- ter engaging surfacesy parallel with theyvedge 'f Jface of said Wedges core.

Y 12; Infan'underreamer, ya body, acutter Y movable longitudinally and transversely with a Y relation to thebody, 'aflongitudinallymovablecutter spreadingvwedg'e inthe body be- Y f hind-the cutter, the cutter and Wedgebeing formed vso that relative movement of thecutj 

